When the Magical Congress of the United States (MACUSA) moved to Washington in 1777, the Great Meeting Chamber there was enlarged for a gathering of thousands of North American witches and wizards to debate whether they owed allegiance to their countries alone, or the international community at large. Since the Revolutionary War was raging at the time, the group also discussed whether they should help the Colonial No-Maj in their fight against the British Muggles, or stay on the sidelines without intervening (Pm:MACUSA).
A message was sent to the Ministry of Magic in London asking if they were going to intervene in the war, and the return answer was “Sitting this one out,” to which President McGilliguddy replied tersely, “Mind you do.” In the end, the American magical community officially remained neutral, but unofficially they helped protect the No-Maj and win victory over the British. Afterward, witches and wizards also celebrated Independence Day, though their celebrations were separate from the No-Maj (Pm:MACUSA).
From the Web
Pottermore: Magical Congress of the United States (MACUSA) by J.K. Rowling